Why do heavy equipment trailers have steel over the tires?

[JCoastie]

Why do a lot of heavy duty equipment trailers have steel plates over the tires on an otherwise wood deck?
Is it a usable access point for the axles or something? Am I missing out by my tandem trailer not having that?

Random Example:

 

[WinterDeere]

I always assumed it was to minimize trailer height. Trailer deck + cross members is what... 5" thick? Steel plate is... 1/4" thick? Using those numbers, you can drop the deck height of the trailer by 4.75" with similar axle travel.

I guess cross members could be arranged to straddle the wheels either way, which might take wood decking thickness down to 1.5" on lighter trailers, but what's the wood deck thickness on a heavier trailer?

 

[JCoastie]

interesting, never though of that aspect

 

[oldnslo]

Just musing but would there be a concern about potential for wood deck to collapse and puncture the tires Vs steel plate? Would a tire loosing the tread damage wood deck vs steel?

Winterdeere probably has the most logical answer

 

[two_bit_score]

Is it a usable access point for the axles

I've often wondered the same thing.

 

[CliffordK]

I have fenders rather than a deckover. I have considered drive-over fenders, say 2" to 4" above the deck.

I agree with @WinterDeere that it is all about minimizing trailer height. I suppose it also depends on support span. So, over the tires one has about 3 feet of longitudinal unsupported decking. Steel is thinner, and can be supported from the sides rather than just crosswise.

I suppose there is the rare case of puncturing the deck, but if that happens one has other issues to deal with. I think there are some drive-over styles that has the equipment actually driving on the tires. Perhaps some older lowboys.

 

[jaxs]

Probably just good practice based on experience by manufactures that concern themselves with such. In addition to clearance already mentioned, boards will be continuedly coated with mud which in turn rots before remainder of boards.

 

[D&D]

The plates are supposed to be load bearing and provide for adequate tire clearances.

 

[rangerfredbob]

I'm pretty sure it's just for tire clearance, metal is thinner and fine in a small area like that... 2" is 2"...

 

[LD1]

Its just to lower the deck.

Allthough crossmembers arent over the tires so that thickness is negligable.

1/4" plate versus 1-1/2" lumber. Can lower the deck 1-1/4" and still maintain tire clearance.

Same concept of "pierced" beam deckovers. Rather than the crossmembers being ON TOP of the I-beam, the run through. It also saves a couple of boards per trailer. These are the trailers where you see the top of the I-beam on the surface of the trailer as if it was a deck board itself